Data transmission in the copper twisted pair generally takes place over what is called a differential mode (DM) system. In the DM, the difference of the voltage between the two wires with respect to ground is transmitted while a two port loop is formed joining a transmitter, a receiver and the two twisted wires. Due to the imperfect twisting of the two wires, there is a leakage of the DM signal into what is known as the Common Mode (CM), with respect to the reference ground. The common mode voltage can be tapped from the center of the transformer at the DM transmitter or at the DM receiver with respect to the physical ground. The ground constitutes the return path of the CM signal carried by the two wires and joining the CM transmitter and receiver CM impedance and sensed through the center tap of the differential mode receiver with respect to ground.